This invention relates generally to apparatus for producing coal-oil mixtures, and, more particularly, to apparatus for on-line production of coal-oil mixtures at varying output rates in response to a variable demand.
Generally, a coal-oil mixture (COM) is a hybrid fuel consisting of pulverized coal suspended in Number 4 or 6 fuel oil. The coal content of a typical COM may be as high as approximately 55 percent by weight of 80 percent minus 200 mesh coal.
Use and development of COM began in the late 1800's and has continued on a sporatic basis until recently. When world oil shortages prompted more intense interest. Presently, COM is being considered as an alternate fuel in boilers, blast furnaces, and kilns, as well as other applications.
A major problem with using coal-oil mixtures as fuel is the stability of the mixture. That is, without continued agitation of the COM the coal comes out of suspension and settles to the bottom of storage vessels. Such continuous agitation of stored COM is costly in terms of both energy and equipment.
A number of factors relate to the stability of the coal in the coal-oil mixture.
It is evident that the finer the coal is pulverized, the greater the stability of the coal-oil mixture. However, the finer coal is pulverized, the greater the possibility of explosion hazards attendant with pulverizing, storing, and handling of the coal. In addition, although COM made with very fine grinds of coal, may have better stability, the power cost to pulverize the coal to smaller particle size may not be economically feasible. High coal concentration in a COM is desirable from the standpoint of providing a cheaper fuel, however, coal settling may be more difficult to prevent.
A significant market for COM exists in blast furnace and kiln applications such as, for example, those used in the hot metal and pelletizing industries. In fact, based on 1976 figures for annual hot metal and pellet production, an estimate of fuel consumption for these two applications is approximately 7.1.times.10.sup.6 gallons per day of fuel oil. If a hybrid fuel, utilizing as little as 40 percent coal in a COM were used in lieu of straight fuel oil, approximately 24 million barrels of fuel oil per year could be replaced by COM.
In operation, blast and kiln furnaces may require a sizable fuel surge capacity of start up, and experience frequent shut-downs during production or for maintenance.
COM produced at a fixed location and either tanked or piped to blast and kiln furnaces is not suitable because of required storage of the fuel before use. As previously mentioned, users experiencing frequent shut-downs and a variable demand or surge requirement, may require the COM to be stored over periods of time during which the coal settles from the oil, rendering the COM unusable without resuspension of the coal.
Significant efforts have been made to stabilize coal-oil mixtures. These efforts include the addition of various types of agents to the COM in order to prevent the coal from settling during the storage period. A primary disadvantage of this method of stabilizing COM is the cost of such additives. Additional efforts have been made using ultrasonic techniques to form coal-oil dispersions which are stable over extended periods but these too have yet to be proven successful.
Hence, there is need for an apparatus that can supply COM at variable rates to blast furnaces and the like while eliminating large storage tanks and the use of expensive additives and apparatus for stabilizing the COM. A further use and advantage of the apparatus, when configured for transfer from site to site, is for producting a temporary supply of COM for use in evaluating the feasibility of using COM in various types of pre-existing fuel burning apparatus.